The present invention relates generally to heating, ventilation and air conditioning (HVAC) systems for vehicles, and more particularly to thermal storage for HVAC systems in vehicles.
Some hybrid vehicles do not have the capability to provide air conditioning comfort when the engine is off. To improve the overall fuel economy of the vehicles, however, it is generally preferable to have the engine off as often and as long as possible. Nonetheless, not having continuous air conditioning capability may be unsatisfactory to vehicle occupants as compared to conventional vehicles where the engine runs all of the time-allowing for air conditioning whenever desired.
In order to address this concern, some have proposed systems for hybrid vehicles that provide air conditioning even when the engine is off. For example, some hybrid vehicles include refrigerant compressors that have their own electric motor to drive them so they can be driven independently of the engine. Others not only have a separate motor to drive the refrigerant compressor, but also incorporate a dual drive mechanism where the compressor can be electrically driven and also be driven directly off of the accessory drive belt of the engine. However, both of these solutions add to the weight and cost of the vehicle due to the addition of the extra compressor motor as well as the electronics and cables to operate the motor.
Still others have attempted to alleviate this concern by providing refrigerant thermal storage systems and/or secondary loop coolant systems that allow for air conditioning comfort during engine off vehicle operation. While thermal storage and/or secondary loop systems may be employed in the air conditioning systems, a need arises to minimize the cost and packaging space required to operate the air conditioning system under engine-off vehicle operating conditions while still maximizing the fuel economy benefit achieved with hybrid vehicles. That is, an air conditioning system that only provides for short engine-off operation may minimize the cost of the system, but may significantly reduce the fuel economy improvement of the hybrid vehicle, while an air conditioning system that allows for long engine-off operation may be cost prohibitive for certain hybrid vehicles.
In addition, for conventional engine driven vehicles, there may be a desire to provide a HVAC system with a secondary loop and thermal storage. For example, in vehicles where the refrigerant compressor is turned on and off to control capacity at light loads, thermal storage may allow the compressor to remain off for longer periods. This may improve the fuel economy. Again, though, it is desirable to minimize the cost and packaging space while maximizing the fuel economy benefit.